There has been widely practiced anodizing that forms an anodized film on a surface of a member including a substrate of aluminum, aluminum alloy, or the like to improve plasma resistance and gaseous corrosion resistance of the substrate. For example, a vacuum chamber used in a plasma treatment apparatus of semiconductor manufacturing equipment or each of various components provided within the vacuum chamber is typically composed of aluminum alloy. However, if the aluminum alloy is used while being untreated (solid), its properties such as plasma resistance and gaseous corrosion resistance cannot be maintained. An anodized film is therefore provided on a surface of the member composed of aluminum alloy to improve plasma resistance, gaseous corrosion resistance, and the like.
In recent years, power to be applied for plasma generation increases with increase in plasma density due to narrowed interconnection width. In existing anodized films, therefore, dielectric breakdown may be induced by high temperature and high voltage occurring at high power application. Electric properties of the film are varied in a portion where such dielectric breakdown occurs, and therefore the film is less uniformly etched or formed in the portion. The anodized film is therefore desired to be improved in crack resistance and withstand voltage characteristics.
Various techniques have been previously proposed in order to improve properties of the anodized film. For example, PTL 1 suggests that pore size on a surface side of an anodized film is controlled to be small on a side near a film surface and large on a side near a substrate, thereby the anodized film is reduced in reactivity to plasma so as to improve plasma resistance. Such an anodized film can be extremely improved in plasma resistance compared with existing anodized films. In such an anodized film, however, cracking (hereinafter sometimes referred to as “curved-portion cracking”) may also occur in a curvature portion (curved portion) that may exist in actual equipment. This may lead to an environment under which the substrate and the anodized film are each easily corroded.